Inputs of Total and Labile Dissolved Metals from Six Facilities Continuously Discharging Treated Wastewaters to the Marine Environment of Gran Canaria Island (Canary Islands, Spain).

Marta Rodrigo Sanz,Vanessa Millán Gabet,Jean-Louis Gonzalez

doi:10.3390/ijerph182111582

Abstract

The presence of ten metals (Cd, Ni, Pb, Cr, Cu, Zn, Al, Fe, Mn, and Co) was investigated in the final discharge of six facilities, including four wastewater treatment plants, which were continuously discharging treated wastewater to the coastal environment in Gran Canaria Island. A four-day sampling campaign was carried out at each facility in July 2020, in which both the spot samplings technique and the diffusive gradient in thin-film technique (DGT) were carried out to measure total dissolved metals and the in situ labile metal fraction, respectively. After the necessary sample preparation steps, measurements were carried out by ICP-MS for both samplings. Raw data referred to the spot total dissolved and DGT-labile metal concentrations were reported. In general, the average metal concentrations were dispersed in a broad range. As expected, the highest metal contents were found in those facilities with larger industrial contributions. The values of annual average environmental quality standards (AA-EQS) were used to assess the total dissolved metal concentrations for every metal in every final discharge. In only one of the studied facilities, some metals (Ni and Zn) exceeded these EQS within the receiving waterbody, highlighting the need for more efficient treatment targeted towards a specific discharging-water quality. In addition, the total dissolved and labile metal daily fluxes of discharge were calculated to estimate the contribution of every effluent to the receiving water bodies.

Highlights

A significant proportion of metals enter marine water bodies via surface runoff and municipal or industrial wastewater discharges, which are important secondary sources of these substances
We did not observe any difference between the exposed diffusive gradient in thin-films (DGT) and the laboratory blanks for this metal, so this result was not taken into consideration
Note that concentrations of the DGT-measured labile metals shown in Table 2 are the mean values of the 3 exposed replicates, whereas, in the total dissolved fraction, results are the mean values of 3 spot-samples that represented temporal variations during the DGT-deployment

Summary

Introduction

A significant proportion of metals enter marine water bodies via surface runoff and municipal or industrial wastewater discharges, which are important secondary sources of these substances. Wastewater treatment plants (WWTP), due to their high continuous flow rates, discharge important amounts of trace metals and other contaminants into the marine environment, which cannot be fully retained in these facilities [1,2,3]. Other types of facilities continuously discharge treated wastewaters with trace metals to the sea, such as thermal power plants, marine aquaculture, and desalination plants, etc. Its quality impacts tourism, which is the main economic activity, and the seawater intake of desalination plants that provide water for human consumption to most of the island’s inhabitants, in the case of Gran Canaria. The deterioration of seawater quality is crucial and critical

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Conclusion